The present invention relates generally to data storage system head sliders. More particularly, the present invention relates to a head slider having an internal accelerometer for providing improved servo performance and shock sensing.
In magnetic disc drive data storage devices, digital data are written to and read from a thin layer of magnetizable material on a surface of one or more rotating discs. Write and read operations are performed through a transducer which is carried in a slider body. The slider and transducer are sometimes collectively referred to as a head, and typically a single head is associated with each disc surface. When the transducer is a magnetoresistive (MR) type sensor, the combination of the slider and the transducer are frequently referred to as an MR head. The heads are selectively moved under the control of electronic circuitry to any one of a plurality of circular, concentric data tracks on the disc surface by an actuator device. Each slider body includes an air bearing surface (ABS). As the disc rotates, the disc drags air beneath the ABS, which develops a lifting force that causes the head to lift and fly several microinches above the disc surface.
The performance of disc drives is highly dependent upon the performance of the track following servo system. Conventional disc drives use a position only feedback system. As the magnetic track widths are reduced, it becomes increasingly difficult for the servo system to perform. If the servo is overdamped, the response time is compromised. If the servo is underdamped, servo over shoot can occur causing degraded servo performance.
It is possible to use the actuator input current as a measure of force and acceleration. However, the actuator coil is located at the end of the load arm carrying the recording head. Along this distance, there are mechanical loss points due to hysteresis and stick slip (the force required to overcome static friction before the bearings move). Therefore, better methods of measuring force and acceleration of the head slider are desired.
Currently, some disc drives such as those used in mobile computer applications are built with shock sensors in the drive to provide data integrity. For example, if the disc drive is given a mechanical shock during operation, it is possible that data will be incorrectly written on the disc. The shock, if large enough, can cause the head to move off track. If the disc drive is writing data at the time of the shock, the head will write this data over an adjacent track. Then, when an attempt to retrieve the data is made, it will not be found in the intended location. Additionally, it is likely that the data will have been written in an area where other data previously existed. To prevent this occurrence, the mobile class of disc drives incorporate the separate shock sensors into the disc drive.